Silicon sensors are extensively used in a large and increasingly varied field, including important areas such as medical instrumentation, automotive applications such as engine control and tyre pressure monitoring, industrial process control and the avionics industry. The most commonly used conversion principles for silicon based sensors are capacitive detection and piezoresistive detection.
Piezoresistive sensors are generally considered to be more robust than capacitive sensors. Another advantage is that they give an output signal proportional to the input with good linearity. Capacitive sensors, on the other hand, have the advantage over the piezoresistive type in that they consume less power, but have a non-linear direct output signal and are more sensitive to electromagnetic interference. Capacitive silicon sensors can be made to be small in size and can easily be made by surface micromachining. However, they are not very robust and their pressure sensitive diaphragm needs to be protected against the pressure media by a gel or, other flexible material in most applications. This results in an increase in vibration sensitivity due to the mass added to the top of the diaphragm. Advanced and well proven methods of manufacturing silicon pressure sensors and inertial sensors are described in the patent publications EP-A-742581 and EP-A-994330, but these have the problems mentioned above.